11-11-17 P - Organic Chemistry (Mcmurry)

Question

What stereochemistry do you expect for the alkene obtained by E2 elimination of (1R, 2R)-1,2-dibromo-1,2-diphenylethane? Draw a Newman projection of the reacting conformation.

Step-by-Step Solution

Answer

The stereochemistry for the alkene by E2 elimination of (1R, 2R)-1,2-dibromo-1,2-diphenylethane is,

Newman projection

Newman projection is a conformation where a dot does the representation of the front atom and the back atom is represented by a circle. The front atom is proximal, and the back atom is distal.

The Newman projection of the reacting conformation

The Newman projection of the reacting conformation 

      (1R, 2R)-1,2-dibromo-1,2-diphenylethane

This reactant is converted into a Newman projection, and the conformation for anti-periplanar geometry for –H and –Br is drawn as,

                          Newman projection

By E2 elimination, the alkene formed is (Z)-1-bromo-1,2-diphenylethylene

                   (Z)-1-bromo-1,2-diphenylethylene